JP4359228B2 - Magnetic recording element, magnetic recording apparatus, and magnetic recording method - Google Patents

Description

  The present invention relates to a magnetic recording element capable of controlling the magnetization direction of a magnetic material by flowing spin-polarized electrons and recording information, a magnetic recording device using the same, and a magnetic recording device using the magnetic recording device The present invention relates to a recording method, and more particularly, to a magnetic recording element or the like characterized by performing multi-value recording in which information larger than 1 bit is recorded in one memory cell.

  In recent years, as a presence that supports and leads a wide and highly informatized society, information recording technology that satisfies various requirements has been demanded. A magnetic recording device using the magnetic moment of a ferromagnetic material is widely used as, for example, a hard disk drive, and proposed as a magnetic random access memory (MRAM) having both high speed and non-volatility.

  Recently, the demand for higher density has reached a length scale of 100 nanometers to several tens of nanometers or less as a unit cell for storing 1-bit information, and there is a technical barrier in the information writing system. In the current magnetic field writing method used in hard disk drives and MRAMs, as the memory cell size is reduced, the amount of current for generating a magnetic field required for writing increases, as well as malfunctions in adjacent cells (crosstalk). ) Is inevitable.

The current direct drive magnetization reversal phenomenon described in Non-Patent Document 1 is expected to provide a new magnetic recording technique capable of solving the problem of the current magnetic field writing method. This phenomenon is caused by the action and transmission of the spin angular momentum of conduction electrons to the magnetization of the magnetic material when the flow of electrons spin-polarized in a direction antiparallel to the magnetization direction of the magnetic material passes through the magnetic material. This is to cause magnetization reversal using torque. By using this phenomenon, it is possible to exert a more direct effect on a nanoscale magnetic material as compared with magnetization reversal by a current magnetic field. Therefore, crosstalk does not occur and high-speed magnetization reversal can be expected. Another advantage is that the amount of current required for writing decreases as the cell size decreases.
FJ Albert et al., Appl. Phys. Lett., 77, 3809 (2000)

  As described above, by using the direct current driving method, writing to a nanoscale memory cell becomes possible, but there is always a potential demand for further higher recording density. Also, assuming that the memory cells are arranged in an array and connected to the wiring, and used as a high recording density MRAM, not only the recording element portion but also the peripheral portion of the recording element such as a transistor for circuit selection is miniaturized. I need it. However, since miniaturization of the transistor size is limited, a great effect can be expected if a recording apparatus that requires a smaller number of transistors for the same recording capacity can be manufactured.

  The present invention has been made on the basis of recognition of such a problem, and an object of the present invention is to use magnetic reversal by direct current drive as a writing method and to record a plurality of bits of information on one element. It is an object of the present invention to provide a recording element, and a magnetic recording apparatus and a magnetic recording method that realize high recording density using the recording element.

  In view of the above circumstances, the first of the present invention has a magnetic layer (recording layer) having a variable magnetization direction, and is injected with spin-polarized electrons, depending on the direction of the flow of spin-polarized current. A magnetic recording element capable of recording information corresponding to the magnetization direction with a change in magnetization direction, and formed on a first magnetic layer (recording layer) having a variable magnetization direction and the first recording layer. A first nonmagnetic layer, a pinned layer formed on the first nonmagnetic layer and including a magnetic material, the magnetization direction of which is pinned, and a second nonmagnetic layer formed on the pinned layer And a second magnetic layer (recording layer) formed on the second nonmagnetic layer and having a variable magnetization direction, and the positive and negative reversal current critical values of the first magnetic layer are set to Ic (1 +), Ic (1 ;-), and the positive and negative reversal current critical values of the second magnetic layer are Ic (2; +), Ic (2 ;-) Ic (1; +)> Ic (2; +) and | Ic (1 ;-) |> | provide a magnetic recording element, characterized in that a is | Ic (2 ;-).

  Such a magnetic recording element of the present invention can be applied to a magnetic recording apparatus or the like.

The second aspect of the present invention has a magnetic layer (recording layer) having a variable magnetization direction, in which spin-polarized electrons are injected, and the magnetization direction changes according to the direction of the spin-polarized current flow. A magnetic recording element capable of recording information according to the magnetization direction, wherein the first magnetic layer (recording layer) has a variable magnetization direction, and the first magnetic layer is formed on the first recording layer. A nonmagnetic layer; a pinned layer formed on the first nonmagnetic layer, including a magnetic material; and having a magnetization direction pinned; a second nonmagnetic layer formed on the pinned layer; 2 and a second magnetic layer (recording layer) having a variable magnetization direction, and the positive and negative reversal current critical values of the first magnetic layer are set to Ic (1; +), If Ic (1 ;−) and the positive and negative reversal current critical values of the second magnetic layer are Ic (2; +) and Ic (2 ;−), Ic (1; )> Ic (2; +) and | Ic (1 ;-) |> | Ic (2 ;-) | satisfying positive write currents Iw (1; +) and Iw (2; +) To a value satisfying Iw (1; +)> Ic (1; +)> Iw (2; +)> Ic (2; +)
Negative write currents Iw (1 ;−), Iw (2 ;−) are set to values satisfying Iw (1; −) <Ic (1; −) <Iw (2; −) <Ic (2 ;−) When writing the data strings b [1] (= 0 or 1) and b [2] (= 0 or 1) in order from the first magnetic layer and the second magnetic layer having a large reversal current, b [ 1] = 0, b [2] = 0 when writing, and when writing b [1] = 1, b [2] = 1, the writing current Iw (1 ;−) is passed. When writing the current Iw (1; +) and writing b [1] = 0, b [2] = 1, first, the write current Iw (1; +) is supplied, and then the write current Iw. In the case of writing (2 ;−) and writing b [1] = 1, b [2] = 0, first, the write current Iw (1 ;−) is supplied, and then the write current is supplied. And a step of flowing a flow Iw (2; +).

  According to the first and second aspects of the present invention, it is possible to record a plurality of bits of data on one recording element in a magnetic recording element using a magnetization reversal by injection of a spin-polarized current as a writing method. In addition, a magnetic recording apparatus that realizes high-density recording can be provided by using this magnetic recording element.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the drawings. In addition, the same code | symbol shall be attached | subjected to the structure which is common throughout embodiment and an Example, and the overlapping description is abbreviate | omitted. Each drawing to be referred to is a schematic diagram for promoting explanation and understanding of the invention. For convenience of drawing display, there are places where shapes, dimensions, ratios, and the like are different from the actual apparatus. The design can be changed as appropriate in consideration of known techniques.

(First embodiment)
A magnetic recording element according to the first embodiment of the present invention will be described. The magnetic recording element according to the first embodiment is a magnetic recording element capable of storing 2-bit data.

<Element structure>
FIG. 1 is a diagram schematically showing a cross-sectional structure of the magnetic recording element 10 according to the first embodiment. In this magnetic recording element, a ferromagnetic layer FF1, a nonmagnetic layer SL1, a ferromagnetic layer FP1, a nonmagnetic layer SU2, and a ferromagnetic layer FF2 are stacked in this order on a substrate with or without a nonmagnetic layer. Is. The planar shape of the magnetic recording element 10 is, for example, a square, and the three-dimensional shape of the element 10 in this case can be a square pillar or a truncated pyramid. Although not explicitly shown in FIG. 1, an electrode layer can be provided above FF1 and below FF2. Note that the ferromagnetic layer FP1 and the ferromagnetic layers FF1 and FF2 may have a laminated structure including a plurality of sublayers as described later.

  First, the case where the ferromagnetic layers FP1, FF1, and FF2 are single layers will be described.

  The ferromagnetic layer FP1 is made of a ferromagnetic material. The magnetization direction of the ferromagnetic layer FP1 is fixed in the film plane and does not change even under the influence of the electron current. This magnetization pinning can be performed by using a magnetic material having a very large uniaxial anisotropy constant Ku for the ferromagnetic layer FP1. Or it can carry out by using the film | membrane whose thickness is sufficiently thick compared with FF1 and FF2 for FP1. In addition, when the ferromagnetic layer FP1 has a laminated structure, the magnetization can be fixed by another method, which will be described later as a modified example of the fixed layer. Since the magnetization is fixed in this way, the magnetization of the ferromagnetic layer FP1 does not substantially rotate even under an external magnetic field. Hereinafter, the ferromagnetic layer FP1 is referred to as a fixed layer.

  The ferromagnetic layers FF1 and FF2 are made of a ferromagnetic material. The ferromagnetic layers FF1 and FF2 are not provided with a fixing mechanism. Therefore, the magnetization directions of the ferromagnetic layers FF1 and FF2 can be changed by being influenced by the electron current. Hereinafter, the ferromagnetic layers FF1 and FF2 are referred to as free layers.

Intermediate layer SL1 (SU2), a non-magnetic semiconductor such as Si, non-magnetic metals such as Cu, and the like non-magnetic insulation film SiO _2. The intermediate layer SL1 (SU2) only isolates the pinned layer FP1 and the free layer FF1 (FF2) to such an extent that the direct magnetic interaction between the pinned layer FP1 and the free layer FF1 (FF2) is negligible. Film thickness is required. At the same time, when a current is passed through the device, it is required that the direction of electron spin does not reverse before the conduction electrons transmitted through the pinned layer FP1 reach the free layer FF1 (FF2). ) Must be thinner than the spin diffusion length.

  In the magnetic recording element 1, the magnetization direction of the free layer FF1 faces one of two easy axis directions in the film plane in a state where no current flows. By assigning these to either “0” or “1”, the free layer FF1 can store 1-bit data. Similarly, since 1-bit data can be stored in the free layer FF2, 2 bits of data can be stored per magnetic recording element.

  Which of the possible directions of magnetization of the free layer is “0” or “1” is arbitrary, and the definition of data stored in the free layer FF1 and the free layer FF2 is independent. Therefore, a state in which the magnetization of the free layer FF1 faces in a direction parallel (antiparallel) to the magnetization of the pinned layer FP1 can be defined as “0” (“1”) without losing generality. Further, the state in which the magnetization of the free layer FF2 is directed in an antiparallel (parallel) direction to the magnetization of the pinned layer FP1 can be defined as “0” (“1”) (see FIG. 2). In FIG. 2, the reference numerals shown below the cross-sectional schematic diagrams correspond to any of the four data. Further, as shown in FIG. 2, the positive direction of the current is defined as the direction from FF2 toward FF1. The flow of electrons at this time is in the direction from FF1 to FF2 as shown in FIG. Hereinafter, this definition will be used for explanation.

<Writing method>
A method of writing data in the magnetic recording element 10 will be described. Information is written by flowing an electron stream between the free layers FF1 and FF2.

  First, the case where a current is passed in the positive direction will be described. At this time, the electron flow flows from the free layer FF1 toward the free layer FF2. A part of the electron flow flowing from the free layer FF1 into the fixed layer FP1 passes through the fixed layer FP1 and flows into the free layer FF2, and the rest is reflected and returns to the free layer FF1.

  At this time, the electron flow passing through the pinned layer FP1 and flowing into the free layer FF2 is spin-polarized in a direction parallel to the magnetization direction of the pinned layer FP1, and the magnetization of the free layer FF2 is spin-polarized. Torque is proportional to the current intensity from the electron current. If the magnetization direction of the free layer FF2 before passing the current is antiparallel to the magnetization direction of the pinned layer FP1 (in the case of “0”), if the current intensity is greater than a certain critical value Ic (2, +) The magnetization of the free layer FF2 is reversed and faces the direction parallel to the magnetization direction of the pinned layer FP1. That is, “1” is written. That is, the critical value Ic (2; +) is a value necessary for the magnetization of the free layer FF2 to be directed in a direction parallel to the magnetization direction of the pinned layer FP1 by a positive current (+ direction). If the data stored in the free layer FF2 is “1” before the current is supplied, the data is maintained even if the current is supplied in the positive direction.

  On the other hand, the electron current reflected by the pinned layer FP1 and returning to the free layer FF1 is spin-polarized in a direction antiparallel to the magnetization direction of the pinned layer FP1, and the magnetization of the free layer FF1 is the spin-polarized electron. The torque is proportional to the current intensity from the current. When the magnetization direction of the free layer FF1 before flowing the current is parallel to the magnetization direction of the pinned layer FP1 (in the case of “0”), if the current intensity is a certain critical value Ic (1; +) or more, The magnetization of the free layer FF1 reverses and faces in a direction antiparallel to the magnetization direction of the pinned layer FP1. That is, “1” is written. If the data stored in the free layer FF1 is “1” before the current is supplied, this data is maintained even if the current is supplied in the positive direction.

  The critical value Ic (2; +) and the critical value Ic (1; +) can be made different from each other by selecting the thickness and material of each layer constituting the element. The selection of such a film thickness and material will be described later. At this time, it is possible to reverse only one of the magnetization directions of the free layer FF1 and the free layer FF2 by flowing a current having a magnitude between these two critical values in the positive direction. The relationship Ic (2; +) <Ic (1; +) can be satisfied, and the relationship Ic (2; +)> Ic (1; +) can be satisfied. Let us consider a case in which a current I (> 0) is passed through.

  3 to 10 are diagrams for explaining the current writing process. The sign shown in the left column (represented as “front”) in each figure is the sign of the magnetic recording element 10 before current writing, and the sign represented in the right column (represented as “rear”) is after current writing. The magnetic recording element 10 of FIG.

  When I satisfies I <Ic (2; +), the state change as shown in FIG. 3 occurs before and after the current flows. That is, the magnetization direction does not change before and after the current I flows. When I satisfies Ic (2; +) <I <Ic (1; +), the state change as shown in FIG. 4 occurs (the magnetization state shown in FIG. 2 (a) is the magnetization state of FIG. 2 (b)). Change to state). When I satisfies I> Ic (1; +), the state change as shown in FIG. 5 occurs (the magnetization state shown in FIG. 2A changes to the magnetization state shown in FIG. 2D). .

  Next, a case where a negative current (I <0) is supplied will be described. In this case as well, two critical values Ic (1; −) <0 and critical value Ic (2; −) <0 can be defined based on the same principle, and a current exceeding the critical value flows (| I |>) | Ic (1; −) | or | I |> | Ic (2; −) |), the magnetization direction of the free layer FF1 or the free layer FF2 can be reversed.

  When the relationship | Ic (1; −) | <| Ic (2; −) | is satisfied, the state change diagram when the current is flowed in the negative direction is represented by | I | <| Ic (1; −) | 3 and when | Ic (1; −) | <| I | <| Ic (2; −) | When I> Ic (2; −), the result is as shown in FIG. Therefore, when Ic (2; +) <Ic (1; +) and | Ic (1; −) | <| Ic (2; −) | are satisfied, the five state changes shown in FIGS. It can be seen that it can be used as a ternary magnetic recording element. However, since there is no change from a state other than “10” to “10” among these state changes, in this case, it cannot be used as a recording element having four values.

  When the relationship | Ic (1; −) |> | Ic (2; −) | is satisfied, the state change when the current is flowed in the negative direction is: | I | <| Ic (2; −) | When FIG. 3 is obtained, when | Ic (2; −) | <| I | <| Ic (1; −) |, FIG. 4 is obtained. When | I |> | Ic (1; −) |, the result is as shown in FIG.

  Therefore, when Ic (1; +)> Ic (2; +) and | Ic (1 ;-) |> | Ic (2 ;-) | are satisfied, five patterns shown in FIGS. State change is possible. In this case, it is possible to change from any of the four states “00”, “01”, “10”, and “11” to another arbitrary state through two state changes. . Since it is not necessary to read the state prior to writing, high-speed and simple writing is possible.

  Specifically, for example, a desired state can be written by the procedure shown in FIG. That is, the relationship Iw (1; +)> Ic (1; +)> Iw (2; +)> Ic (2; +)> 0> Ic (2 ;-)> Iw (2 ;-)> Ic (1 ;-)> Iw (1; +); Iw (2; +); Iw (1 ;-); Iw (2 ;-) is selected. In order to write “00”, a current Iw (1 ;-) is passed. In order to write “01”, first, the current Iw (1 ;−) is supplied, and then the current Iw (2; +) is supplied. In order to write “10”, first, the current Iw (1; +) is supplied, and then the current Iw (2 ;−) is supplied. In order to write “11”, a current Iw (1; +) is passed.

<Reading method>
Next, a method for reading information in the magnetic recording element according to the first embodiment will be described.

  Information stored as the magnetization directions of the free layers FF1 and FF2 can be read using the magnetoresistance effect. The electric resistance when a current is passed between the fixed layer FP1 and the free layer FF1 is higher when the magnetization directions are antiparallel to each other than the value R1 when the magnetization directions are parallel to each other, and can be written as R1 + ΔR1. Similarly, the electric resistance when a current is passed between the pinned layer FP1 and the free layer FF2 is higher when the magnetization directions are antiparallel to each other than the value R2 when the magnetization directions are parallel to each other, and can be written as R2 + ΔR2.

  An example described in the writing section, that is, a case where Ic (1; +)> Ic (2; +) and | Ic (1 ;−) |> | Ic (2 ;−) | When a sense current satisfying Ic (2; −) <I <Ic (2; +) and having a magnitude sufficient to ensure a sufficient output voltage is supplied, if ΔR1 ≠ ΔR2, the free layer FF1 and Depending on the magnetization direction of the free layer FF2, as shown in the schematic cross-sectional view of FIG. 11, the electric resistance takes four different values depending on the recording state. Therefore, reading can be performed by the difference in electric resistance.

<Modified example of fixed layer and free layer>
12 to 26 are schematic views showing cross sections of the fixed layer FP1 and the free layers FF1 and FF2, respectively.

12 to 26, FM is a ferromagnetic sublayer, and FC is a nonmagnetic layer, which is a coupling layer that provides ferromagnetic coupling between two ferromagnetic sublayers FM sandwiching the FM. AC is a nonmagnetic layer, and is a coupling layer that provides antiferromagnetic coupling between two ferromagnetic sublayers FM sandwiching the AC. The arrows in FIGS. 12 to 26 indicate the easy magnetization direction.

  Each of the fixed layer FP1 and the free layers FF1 and FF2 has the internal structure of any one of the schematic cross-sectional views shown in FIGS. The ferromagnetic sublayer FM constituting the fixed layer FP1 and the free layers FF1 and FF2 may have a structure in which a plurality of ferromagnetic films are stacked. That is, the fixed layer FP1 and the free layers FF1 and FF2 are each a single layer film of a ferromagnetic material, a multilayer film in which two or more layers of ferromagnetic films are laminated, or a ferromagnetic sublayer FM and a non-layered film. A multilayer film in which magnetic sublayers FC and AC are laminated. As another example, the fixing layer FP1 has an internal structure of any of the schematic cross-sectional views shown in FIGS. 12 to 26, and the sublayer FM constituting the fixing layer FP1 further has an internal structure. It is also possible to have a structure in which two or more ferromagnetic films and one or more antiferromagnetic films are stacked. However, in this case, among the films constituting the fixed layer FP1, the film in contact with the intermediate layer SU1 and the film in contact with the intermediate layer SL1 need to be ferromagnetic films. Such a laminated structure can be used as a means for fixing the magnetization of the ferromagnetic layer because exchange coupling exists between the ferromagnetic film and the antiferromagnetic film.

  When the fixed layer FP1 and / or the free layers FF1 and FF2 are composed of a plurality of ferromagnetic sublayers FM, the data stored in the free layers FF1 and FF2 is defined as follows, Writing and reading can be performed in a similar manner. The data stored in the free layer FF1 includes the magnetization direction of the ferromagnetic sublayer in contact with the intermediate layer SL1 among the sublayers constituting the fixed layer FP1, and the intermediate layer SL1 among the sublayers constituting the free layer FF1. It is defined as “0” when the magnetization directions of the ferromagnetic sublayers in contact with each other are parallel to each other, and “1” when the magnetization directions are antiparallel. Data stored in the free layer FF2 includes the magnetization direction of the ferromagnetic sublayer in contact with the intermediate layer SU2 among the sublayers constituting the pinned layer FP1, and the intermediate layer SU2 among the sublayers constituting the free layer FF2 layer. It is defined as “0” when the magnetization directions of the ferromagnetic sublayers in contact with each other are antiparallel to each other, and “1” when they are parallel.

  The nonmagnetic sublayers FC and AC constituting the fixed layer FP1 and the free layers FF1 and FF2 play a role of causing interlayer exchange coupling between the ferromagnetic sublayers on both sides adjacent to the nonmagnetic sublayer FC and AC.

In general, interlayer exchange coupling through a nonmagnetic layer vibrates positively and negatively with respect to the film thickness of the nonmagnetic layer as schematically shown in FIG. Therefore, if the film thickness of the nonmagnetic sublayer is set so as to correspond to either the positive or negative peak position in FIG. 27, the ferromagnetic or antiferromagnetic between the adjacent ferromagnetic sublayers on both sides thereof. Exchange coupling occurs. The film thickness of the nonmagnetic sublayer FC that causes the ferromagnetic interlayer exchange coupling may be adjusted to t ₁ in FIG. 27, for example. The film thickness of the nonmagnetic sublayer AC that causes antiferromagnetic interlayer exchange coupling may be adjusted to t ₂ in FIG. 27, for example.

<Modification of structure of magnetic recording element>
For the magnetic recording element of this embodiment, a modified structure as shown in the schematic cross-sectional views of FIGS. 28 to 32 can be used. These are all magnetic recording elements capable of storing, recording and reproducing 2-bit data.

  Each of the ferromagnetic layers in FIGS. 28 to 32 has an internal structure as shown in FIGS. 12 to 26, and is composed of a plurality of magnetic layers, or a laminated structure including a ferromagnetic sublayer FM and nonmagnetic sublayers FC and AC. It can also be a structure. Furthermore, each ferromagnetic sublayer FM may be a laminate of a plurality of magnetic layers. In addition, the ferromagnetic layers FP0, FP1, and FP2 in FIGS. 28 to 32 are each a structure in which each ferromagnetic sublayer FM is laminated with one or more ferromagnetic films and one or more antiferromagnetic films. It can also be. However, in this case, of the films constituting the fixed layers FP0, FP1, and FP2, the films in contact with the intermediate layers SU1, SL1, SU2, and SL2 need to be ferromagnetic films. Such a laminated structure can be used as a means for fixing the magnetization of the ferromagnetic layer as in the case of the ferromagnetic layer FP1 in the element shown in FIG.

  The element shown in FIG. 28 has substantially the same structure as the element shown in FIG. 1, except that the ferromagnetic layer F has magnetization in a predetermined direction, but the magnetization is not fixed. . However, this element also imposes a constraint that the magnetization of the ferromagnetic layer F must not be reversed after recording until the next reproduction.

  FIG. 29 shows a structure in which the nonmagnetic layer SU1 and the ferromagnetic layer FP0 are placed on the ferromagnetic layer FF1 in addition to the stacked structure of FIG. The magnetizations of the ferromagnetic layers FP0 and FP1 are fixed. When the ferromagnetic layers FP0, FP1, and FF1 are single layers, it is desirable that the magnetization directions of FP0 and FP1 are antiparallel to each other. By selecting such a magnetization direction, the torque acting on the free layer FF1 is at least twice that in the case of FIG. 1, and the reversal current can be reduced (see JP 2004-193595). When all or any one of the ferromagnetic layers FP0, FP1, and FF1 has a laminated structure as shown in FIGS. 12 to 28, the same inversion is performed if either of the following two conditions is satisfied. There is an effect of current reduction. These two conditions can be used as a method for controlling the inversion current value.

  The first condition is that the free layer FF1 has the laminated structure of any of FIGS. 12 to 19 and among the sublayers constituting the fixed layer FP0, the ferromagnetic sublayer that is closest to the intermediate layer SU1. And the magnetization direction of the ferromagnetic sublayer closest to the intermediate layer SL1 among the sublayers constituting the pinned layer FP1 are antiparallel to each other.

The second condition is that the ferromagnetic sublayer in which the free layer FF1 has the laminated structure of any of FIGS. 20 to 28 and is closest to the intermediate layer SU1 among the sublayers constituting the fixed layer FP0. And the magnetization direction of the ferromagnetic sublayer closest to the intermediate layer SL1 among the sublayers constituting the pinned layer FP1 are parallel to each other.

  FIG. 30 is a schematic cross-sectional view of a structure in which a nonmagnetic layer SL2 and a ferromagnetic layer FP2 are stacked below the ferromagnetic layer FF2 in addition to the stacked structure of FIG. The magnetizations of the ferromagnetic layers FP1 and FP2 are fixed. For the same reason as above, when the ferromagnetic layers FP1, FP2, and FF2 are single layers, it is desirable that the reversal current can be reduced if the magnetization directions of FP1 and FP2 are antiparallel to each other. Further, when all or any one of the ferromagnetic layers FP1, FP2, and FF2 has a stacked structure as shown in FIGS. 12 to 26, the FP1, FP2, and FF2 are the elements in the structure having the structure shown in FIG. , FP0, FP1, and FF1 satisfy the relationship to be satisfied, and the effect of reducing the inversion current can be obtained.

  In FIG. 31, in addition to the stacked structure of FIG. 1, the nonmagnetic layer SU1 and the ferromagnetic layer FP0 are placed on the ferromagnetic layer FF1, and the nonmagnetic layer SL2 and the ferromagnetic layer FP2 are further provided on the ferromagnetic layer FF2. It is a cross-sectional schematic diagram of the laminated structure. The magnetizations of the ferromagnetic layers FP0, FP1, and FP2 are fixed in a predetermined direction.

  If FP0 and FP1 in FIG. 31 satisfy the relationship to be satisfied by FP0 and FP1 in FIG. 29, there is a similar inversion current reduction effect. Further, if the relationship that FP1 and FP2 in FIG. 30 should satisfy is satisfied by FP1 and FP2 in FIG.

  FIG. 32 has a structure in which the ferromagnetic layer FP1 is removed from the stacked structure of FIG. In this case, by defining the data stored in the free layers FF1 and FF2 as follows, writing can be performed by the method described in the section of writing of the element having the structure of FIG. The data stored in the free layer FF1 is that the magnetization direction of the ferromagnetic sublayer that constitutes the free layer FF1 is located at the bottom of the ferromagnetic sublayer that constitutes the fixed layer FP0. It is defined as “1” when parallel to the magnetization direction and “0” when antiparallel.

  The reading method in each element shown in FIGS. 28 to 32 can be read using the magnetoresistive effect as in the case of the element shown in FIG. That is, it is used that the electric resistance when current flows perpendicularly to the junction surface of each layer is different between the case where the magnetization directions of two ferromagnetic layers in contact with each other through the nonmagnetic layer are parallel to each other and antiparallel.

  In each element shown in FIGS. 1 and 28 to 32, a material having perpendicular magnetic anisotropy may be used for all or part of the ferromagnetic layer. When a material having perpendicular magnetic anisotropy is used for the free layer, the pinned layer in contact with the non-magnetic layer or the ferromagnetic layer F in the element of FIG. 28 also has perpendicular magnetic anisotropy.

<Material and film thickness of each layer>
Next, constituent materials of each layer of the magnetic recording element will be described.

  Co, Fe, Ni or an alloy containing these can be used for the free layers FF1 and FF2. The thickness of the free layer is preferably in the range of 0.6 nm-100 nm.

The materials of the antiferromagnetic layer to fix the magnetization of the pinned layers FP0, FP1, and FP2 are Fe-Mn, Pt-Mn, Pt-Cr-Mn, Ni-Mn, Pd-Mn, Pd-Pt-Mn. Ir-Mn, Pt-Ir-Mn, NiO, Fe ₂ O ₃ , magnetic semiconductors, etc. are preferably used.

Co, Fe, Ni, or an alloy containing these can be used for the fixed layers FP0, FP1, and FP2. In addition, the higher the spin polarizability of the material of the pinned layers FP0, FP1, and FP2, the higher the magnetization reversal efficiency when a current is passed between the pinned layer FP1 and the free layer, which is desirable. Further, at this time, there is an advantage that the MR ratio becomes large and reading becomes easy. Therefore, a high spin polarizability material called half metal is ideal as a material for the pinned layer. Examples of the half metal include a Heusler alloy, a rutile oxide, a spinel oxide, a perovskite oxide, a double perovskite oxide, a zinc blende chromium compound, a pyrite manganese compound, and a sendust alloy. The thickness of the fixed layer FP1 is preferably in the range of 0.2 nm to 50 nm.

  These magnetic materials include Ag, Cu, Au, Al, Mg, Si, Bi, Ta, B, C, O, N, Pd, Pt, Zr, Ir, W, Mo, Nb, H, and the like. By adding a non-magnetic element, the magnetic properties can be adjusted, and other physical properties such as crystallinity, mechanical properties, and chemical properties can be adjusted.

  When the pinned layer FP1 and / or the free layer FF has a multilayer film structure, Cu, Au, Ag, Ru, Ir, Os or any one or more of them is used as the material of the nonmagnetic sublayer constituting the layer. Including alloys can be used.

  According to Non-Patent Document 1, the current for reversing the magnetization of the ferromagnetic layer (reversal current) is proportional to t / g as the efficiency factor g and the thickness t of the free layer. The efficiency factor g depends not only on the spin polarization degree of the material used for the pinned layer and the free layer, but also on the element structure. The element structure is, for example, the number of pinned layers laminated on the free layer via a nonmagnetic layer, and the like, and is a structure that changes the magnitude of torque acting on the free layer. The ferromagnetic layer is different depending on whether the current is passed in the positive direction or the negative direction. Therefore, it is necessary to appropriately adjust the material and film thickness so that the magnitude relationship between the reversal current value of the free layer FF1 and the reversal current value of the free layer FF2 is positive or negative.

  When the magnetization directions of the ferromagnetic layers FP0, FP1, FP2, FF1, and FF2 are oriented perpendicularly to the film surface, the magnetic anisotropy energy density Ku is large and FePt, CoPt, FePd, CoPd exhibiting perpendicular magnetic anisotropy. This can be done using In addition, a magnetic material having a crystal structure of hcp structure (close-packed hexagonal structure) and showing perpendicular magnetic anisotropy can be used. As such a magnetic material, a material containing a metal containing Co as a main component is typical, but other metals having an hcp structure can also be used. In addition, a material exhibiting perpendicular magnetic anisotropy that is an alloy of a rare earth element and an iron group transition element can also be used. Specific examples include GdFe, GdFeCo, TbFe, TbFeCo, DyFe, DyFeCo, and the like. In the case of a laminated structure, Co can be used as a ferromagnetic sublayer constituting the layered structure, and Pt or Pd can be used as a nonmagnetic sublayer.

  When using a non-magnetic metal as the intermediate layer, one of Au, Cu, Cr, Zn, Ga, Nb, Mo, Ru, Pd, Ag, Hf, Ta, W, Pt, Bi, or these An alloy containing any one or more of the above can be used. The thickness of the nonmagnetic metal intermediate layer is preferably in the range of 0.2 nm to 20 nm.

When the intermediate layer functions as a tunnel barrier layer, Al ₂ O ₃ (aluminum oxide), SiO ₂ (silicon oxide), MgO (magnesium oxide), AlN (aluminum nitride), Bi ₂ O ₃ (bismuth oxide) ), MgF ₂ (magnesium fluoride), CaF ₂ (calcium fluoride), SrTiO ₂ (titanium oxide / strontium), AlLaO ₃ (lanthanum oxide / aluminum oxide), Al—N—O (aluminum oxynitride), Si—N -O (silicon oxynitride), a non-magnetic semiconductor (ZnO, InMn, GaN, GaAs , TiO 2, Zn, Te , or them that the transition metal doped) or the like can be used. These compounds do not need to have a completely accurate composition in terms of stoichiometry, and may be deficient or excessive or deficient in oxygen, nitrogen, fluorine, or the like. The thickness of the insulating intermediate layer is preferably in the range of 0.2 nm to 50 nm. By using an insulator for the intermediate layer, it is possible to increase the magnetoresistance ratio and increase the reading efficiency. In this element, since data is read by distinguishing four resistance values, it is preferable to use an insulator intermediate layer in order to ensure sufficient read output.

(Example 1)
As one example of the present embodiment, Examples 1-1 and 1-2 of magnetic recording elements having the cross-sectional structure of FIG. 1 were produced. Although not shown in FIG. 1, an example in which an electrode (wiring) EL1 is provided above the laminated film shown in the drawing and an electrode (wiring) EL2 is provided below is shown below. In the following description, the value to which the unit nm in () is added indicates the film thickness.

Example 1-1
Electrode EL1 (Cu) / Free layer FF1 (Co: 3 nm) / Intermediate layer SL1 (MgO: 0.9 nm) / Fixed layer FP1 (Co: 5 nm / PtMn: 12 nm / Co: 5 nm) / Intermediate layer SU2 (Al ₂ O ₃ : 0.8 nm) / free layer FF2 (Co: t ₂ nm) / electrode EL2 (Cu).

Example 1-2:
Electrode EL1 (Cu) / Free layer FF1 (Co: 3 nm) / Intermediate layer SL1 (MgO: 0.9 nm) / Fixed layer FP1 (Co: 5 nm / PtMn: 12 nm / Co: 5 nm) / Intermediate layer SU2 (Al ₂ O ₃ : 0.8 nm) / free layer FF2 (Ni: 3 nm) / electrode EL2 (Cu)
These magnetic recording elements were produced by the following steps.

  First, the lower electrode EL2 is formed above the wafer. Next, a laminated structure including the free layer FF2, the intermediate layer SU2, the fixed layer FP1, the antiferromagnetic layer AF1, the intermediate layer SL1, and the free layer FF1 is formed on the lower electrode EL2 using an ultrahigh vacuum sputtering apparatus. And further on it is formed. When forming each layer, a target made of a material constituting the layer was used.

The wafer is annealed in a magnetic field in a magnetic field vacuum furnace at 270 ° C. for about 10 hours to impart unidirectional anisotropy to the ferromagnetic layer. An EB (Electron Beam) resist is applied to the film and exposed to EB, and then a mask corresponding to the shape of the magnetic recording element is formed. Next, an area not covered with the mask is etched by an ion milling apparatus. The processing size of the cell is 100 nm × 50 nm. After etching, the mask is peeled off, and SiO ₂ is deposited between the cells using an ultrahigh vacuum sputtering apparatus. Thereafter, the surface was smoothed by ion milling, and “cueing” was performed to expose the surface of the protective film. An upper electrode EL1 is formed on the surface of the protective film. As a result, the magnetic recording element of FIG. 1 was formed.

  Whether or not the obtained embodiment performs the intended operation can be confirmed by measuring the resistance against the amount of current flowing in the direction perpendicular to the bonding surface of each layer. Specifically, it is only necessary to confirm the phenomenon described below.

  First, sweep the current from Imax> 0 to Imin <0, and measure the resistance at each current value. Here, the absolute values of the upper limit IMAX and the lower limit IMIN of the current are sufficiently large (for example, 10 MA). This measurement result typically shows current dependency as shown in FIG. That is, two discontinuous resistance changes occur in the current negative range. The threshold value is IC (<;-), IC (> ;-), and I> Ic (<;-), IC (> ;-) <I <IC (<;-), IC (>;-)> Let the resistance values at I be Ra, Rb, and Rc, respectively.

  Next, the current is swept from Imin <0 to IMAX> 0, and the resistance at each current value is measured. This measurement result typically shows current dependency as shown in FIG. That is, two discontinuous resistance changes occur in the positive current range. The threshold values are Ic (<; +), IC (>; +). The resistance values when I <IC (<; +), IC (>; +) <I are RA and RC, respectively. When the resistance value when IC (<; +) <I <IC (>; +) is Rd, Rb and Rd are different (the magnitude relationship is not important), and Ra and Rc indicate values between them.

  If the above phenomenon can be confirmed, "11" → "01" → "00" → "10" → "11" or "11" → "10" → "00" → "01" → "11" is written. It will be broken.

  Several examples having different thicknesses t2 of the free layer FF2 in the structure of Example 1-1 were prepared, and the above operation was confirmed for each sample. When t2 = 1 nm or t2 = 9 nm, The operation of writing and reading was confirmed. This means that the asymmetry in the film thickness of the two free layers gave a difference in the reversal current. That is, when the thickness of one free layer is smaller than the thickness of the other free layer, the reversal current with the smaller thickness becomes smaller. The reason why the thickness ratio must be greater than 1 is that the reversal of the magnitude relationship in the positive / negative reversal current will occur unless the film thickness is given an asymmetry that exceeds the asymmetry of the positive / negative reversal current. It is.

  Moreover, in the structure of Example 1-2, although the film thicknesses of two free layers were equal, the operation of writing and reading could be confirmed. This means that the difference in the magnetic material used for the two free layers gave a difference in the inversion efficiency. That is, since the free layer FF2 is made of a material having a lower spin polarization than that of the free layer FF1, the inversion current of the free layer FF2 is small.

(Example 2)
As examples of the second embodiment, Example 2-1 of the magnetic recording element having the structure of FIG. 30 and the following materials, and Example 2-2 of the magnetic recording element having the structure of FIG. 31 and the following materials are shown. 2-3 were produced.

Example 2-1: Electrode EL1 (Cu) / Free layer FF1 (Co: 3 nm) / Intermediate layer SL1 (Al ₂ O ₃ : 0.7 nm) / Fixed layer FP1 (Co: 10 nm / PtMn: 10 nm / Co: 5 nm) / Ru: 1 nm / Co: 4 nm) / Intermediate layer SU2 (Cu: 4 nm) / Free layer FF2 (Co: 2.4 nm) / Intermediate layer SL2 (MgO: 0.8 nm) / Fixed layer FP2 (Co: 10 nm / PtIrMn: 20 nm) / electrode EL2 (Cu).

Example 2-2: Electrode EL1 (Cu) / Fixed layer FP0 (IrMn: 18 nm / Co: 10 nm) / Intermediate layer SU1 (MgO: 0.9 nm) / Free layer FF1 (Co: 3 nm) / Intermediate layer SL1 ( Cu: 6 nm) / fixed layer FP1 (Co: 5 nm / Ru: 1 nm / Co: 5 nm / PtIrMn: 13 nm / Co: 12 nm) / intermediate layer SU2 (Al ₂ O ₃ : 0.7 nm) / free layer FF2 (Co: 1 nm) / intermediate layer SL2 (Cu: 4 nm) / fixed layer FP2 (Co: 12 nm / FeMn: 15 nm) / electrode EL2 (Cu)
Example 2-3: Electrode EL1 (Cu) / Fixed layer FP0 (IrMn: 18 nm / Co: 10 nm) / Intermediate layer SU1 (MgO: 0.8 nm) / Free layer FF1 (Co: 3 nm) / Intermediate layer SL1 ( Cu: 6 nm) / fixed layer FP1 (Co: 5 nm / Ru: 1 nm / Co: 5 nm / PtIrMn: 13 nm / Co: 12 nm) / intermediate layer SU2 (Al ₂ O ₃ : 0.7 nm) / free layer FF2 (Co: 2 nm / FeNi: 1 nm) / intermediate layer SL2 (Cu: 4 nm) / fixed layer FP2 (Fe ₃ O ₄ : 12 nm / FeMn: 15 nm) / electrode EL2 (Cu)
With respect to the obtained sample, the operation of writing and reading could be confirmed by the determination method described in Example 1.

  In Example 2-1, there is a difference in the film thickness of the free layer, but the magnitude relationship between the positive and negative reversal currents was maintained even if there was no difference in film thickness as seen in Example 1-1. . This is explained as follows. In Example 2-1, the ferromagnetic layer in contact with the free layer FF1 through the nonmagnetic layer is only one layer of FP1, whereas the ferromagnetic layer in contact with the free layer FF2 through the nonmagnetic layer is FP1. There are two layers of FP2. Therefore, in each of the case where the current flows in the positive direction and the case where the current flows in the negative direction, the free layer FF2 receives a higher efficiency spin transfer torque than the free layer FF1, and the inversion current becomes smaller.

  That is, a structure in which asymmetry exists between the two free layers as shown in FIG. 30 can be said to be an advantageous structure for carrying out the present invention. The asymmetry between the two free layers mentioned here is as follows in detail. As shown in FIG. 30, the entire space is divided into two partial spaces by the plane L1 having the free layer FF1 and the common point. Of the two subspaces, the one that does not include the other free layer FF2 is Σ (1, A), and the one that includes it is Σ (1, B). Similarly, the entire space is divided into two partial spaces by a plane L2 having a common point with the free layer FF2. Of the two subspaces, the one that does not include the other free layer FF1 is Σ (2, A), and the one that includes it is Σ (2, B). At this time, the fixed layer does not exist in Σ (1, A), but the fixed layer FP1 exists in Σ (2, A).

  In Example 2-2, since the film thicknesses of the free layer FF1 and the free layer FF2 were different, different inversion currents were obtained. In Example 2-2, since the free layer FF2 has a smaller film thickness, the inversion current becomes smaller.

  In Example 2-3, different inversion currents were obtained due to asymmetry in the upper half and lower half of the element derived from the material. In Example 2-3, since the free layer FF2 is in contact with the ferromagnetic layer (fixed layer FP2) having a high spin polarization rate via the nonmagnetic layer, it receives a highly efficient spin transfer torque, Therefore, the reversal current is reduced.

(Second Embodiment)
The magnetic recording element according to the second embodiment of the present invention has n (> 2) free layers per element, and can record n-bit data. Hereinafter, such a magnetic recording element will be described with reference to the drawings.

<Element structure>
FIG. 35 is a schematic sectional view (partially omitted) of the magnetic recording element according to the second embodiment. The magnetic recording element 20 has a structure in which ferromagnetic layers FP and FF and nonmagnetic layers SU and SL are alternately stacked. Among them, the ferromagnetic layer includes a layer in which magnetization is fixed (fixed layer FP). Layers with variable magnetization (free layers FF) are alternately arranged. Although omitted in FIG. 35, as a means for fixing the magnetization direction of the fixed layer, an antiferromagnetic layer may be disposed between the fixed layer and the nonmagnetic layer. Alternatively, as another means for fixing the magnetization direction of the pinned layer, a material having a coercive force strong enough to prevent the magnetization from being reversed by an electron current can be used for the pinned layer.

  Each of the ferromagnetic layers may have an internal structure as shown in FIGS. 12 to 19 and FIGS. 20 to 26. Furthermore, the sub-layer constituting the ferromagnetic layer may have a structure in which a plurality of ferromagnetic layers are stacked.

  When there are n free layers FF, it is possible to store n-bit data for each magnetic recording element. For each of i = 1, 2, ..., n, the i-th free layer located from the top is called FF (i) and is located above the upper and lower nonmagnetic layers in contact with FF (i) The nonmagnetic layer is called SU (i), and the underlying nonmagnetic layer is called SL (i). The pinned layer in contact with the nonmagnetic layer SU (i) is referred to as FP (i-1), and the pinned layer in contact with the nonmagnetic layer SL (i) is referred to as FP (i). SU (1) and FP (0) may not exist. SL (n) and FP (n) may not be present.

  When the free layer FF (i) has a laminated structure as shown in FIGS. 12 to 19, in the structure of FIG. 35, the magnetization direction of the lowest layer among the ferromagnetic sublayers constituting the fixed layer FP (i-1). It is desirable that the uppermost one of the ferromagnetic sublayers constituting the fixed layer FP (i) is fixed so that the magnetization directions thereof are antiparallel. By arranging the magnetization directions in this way, the reversal current of the free layer FF (i) can be reduced.

  When the free layer FF (i) has a stacked structure as shown in FIGS. 20 to 26, the magnetization direction of the lowermost one of the ferromagnetic sublayers constituting the fixed layer FP (i-1) in the structure of FIG. Of the ferromagnetic sublayers constituting the fixed layer FP (i), it is desirable that the uppermost one is fixed so that the magnetization directions thereof are parallel to each other. By arranging the magnetization directions in this way, the reversal current of the free layer FF (i) can be reduced. Note that the stacking order of FIG. 35 may be reversed.

<Write>
The data writing method of the magnetic recording element according to the present embodiment is performed by passing a current in a direction perpendicular to the film surface, as in the case of the first embodiment.

  For each of i = 1, 2,..., n, when a sufficiently large current is passed in the positive direction (the direction from the bottom to the top in FIG. 35), the magnetization direction of the free layer FF (i) is a certain direction. It turns in the direction opposite to the first direction when a sufficiently large current is passed in the negative direction (the direction from the top to the bottom in FIG. 35). Data stored in the free layer FF (i) is defined as “1” when the magnetization direction of the FF (i) is in the first direction, and “1” when the magnetization direction is in the opposite direction to the first direction. Details of writing when it is defined as “0” will be described below.

  By flowing the current I (> Ic (i; +)> 0), the data stored in the free layer FF (i) is inverted from “0” to “1”. Further, by flowing the current I (<IC (I; −) <0), the data stored in the free layer FF (I) is inverted from “1” to “0”. In order to make it possible to write 2 <SUP> n values arbitrarily with this magnetic recording element, for any i, j (where i ≠ j), Ic (i; +)> If Ic (j; +), then | Ic (i ;-) |> | Ic (j ;-) | ”is a necessary and sufficient condition.

  Because, for some I, j (where i ≠ j), Ic (i; +)> Ic (j; +) and | Ic (i ;-) | <| IC (J ;-) | Or IC (I; +) <IC (J; +) and | IC (I ;-) | <| IC (J ;-) | in the writing section of the first embodiment This is because, among the 2 <SUP> n values, a value that cannot be written occurs.

“If Ic (i; +)> Ic (j; +) for any I, j (where i ≠ j), then | Ic (i ;-) |> | Ic (j ;-) |” For example, 2 ⁿ values can be arbitrarily written by the following procedure.

  First, σ1, σ2,…, σn are obtained by rearranging 1,2,…, n from the one with the larger inversion current to the one with the smaller inversion current (Ic (σ1; +)> Ic (σ2; +)>… > Ic (σn; +) and | Ic (σ1 ;-) |> | Ic (σ2 ;-) |> ...> | Ic (σn ;-) |).

  The current values Iw (1; +), Iw (2; +), ..., Iw (n; +) are changed to Iw (1; +)> Ic (σ1; +)> Iw (2; +)> Ic (σ2; +)>…> Iw (n; +)> Any value satisfying Ic (σn; +). Iw (1 ;-); Iw (2;-)>…> Iw (n ;-), Iw (1 ;-) <Ic (σ1 ;-) <Iw (2 ;-) <Ic (σ2 ;-) <… <Iw (n ;-) <Ic (σn ;-)

  Data b [1] (= 0 or 1), b [2] (in order from the free layer with the largest reverse current (in order of the free layer FF (σ1), FF (σ2), ..., FF (σn)) = 0 or 1), ..., b [n] = (0 or 1) is written.

First, b [1], b [2],... Are sequentially written to obtain a bit string b = b [1] b [2]... B [n] in which n pieces of 0 or 1 are arranged. (Hereinafter, an example of writing n = 6 and b = 110001 will be described together for the sake of concrete explanation.)
Next, the bit string b is divided for each partial sequence (referred to as a block) having the same value. When A is the number of blocks, 1 ≦ A ≦ n. (For example, b = 110001 can be divided into three blocks, 11/000/1. That is, A = 3.)
The head position of the a-th block (a = 1, 2,..., A) can be designated by counting from the head of the entire bit string b, which is denoted as m (a). (In the above example, m (1) = 1, m (2) = 3, m (3) = 6.)
At this time, if the beginning of the bit string is 1 (that is, b [1] = 1), Iw (m (1) = 1; +), Iw (m (2) ;-), Iw (m (3); Data corresponding to bit string b can be written by passing current A times in the order of +),. (Example: Iw (1; +); Iw (3 ;-); Iw (6; +))
If the beginning of the bit string is 0 (that is, b [1] = 0), Iw (m (1) = 1 ;-), Iw (m (2); +), Iw (m (3);- ),...,...,.

<Read>
As in the case of the first embodiment, the method of reading data in this element is performed by passing a current in a direction perpendicular to the film surface and using the magnetoresistance effect. Depending on the magnetization direction of the free layer FF (i), the electrical resistance between the pinned layer FP1 (i-1) and the pinned layer FP1 (i) is R (i) or R (i) + ΔR (i). Here, for any integer x satisfying 0 ≦ x ≦ 2 ⁿ −1, the number in the i-th digit when x is represented in binary is defined as b (x, i) (b (x, i) ) = 0 or 1). Furthermore, the function r (x) of the equation (1) indicating the electric resistance of the element is defined using the function b (x, i).

It is necessary to select the material, film thickness, structure, etc. so that the elements have 2 ⁿ resistance values different from each other, that is, r (0), r (1), ..., r (2 ⁿ -1) are different from each other. . It should be noted that the intensity Is of the sense current during reading satisfies maxIc (1;-), ..., Ic (n;-) <Is <minIc (1; +), ..., Ic (n; +) Take.

(Example 3)
As Example 3 of this embodiment, a recording element (sample 1) capable of 3-bit recording was manufactured. Example 1: Electrode EL1 (Cu) / Free layer FF1 (Co: 2.5 nm) / Intermediate layer SL1 (Al ₂ O ₃ : 0.7 nm) / Fixed layer FP1 (Co: 4 nm / Ru: 1 nm / Co: 4 nm) / IrMn: 15 nm / Co: 9 nm) / Intermediate layer SU2 (Cu: 4 nm) / Free layer FF2 (FeNi: 2 nm) / Intermediate layer SL2 (MgO: 0.6 nm) / Fixed layer FP2 (Co2CrAl: 10 nm / PtMn: 14 nm) / Co2MnSi: 12 nm) / Intermediate layer SU3 (MgO: 0.8 nm) / Free layer FF3 (Co: 2 nm / CoFeNi: 1 nm) / Intermediate layer SL3 (Cu: 5 nm) / Fixed layer FP3 (CoFe: 10 nm / PtIrMn: 18 nm) ) / Electrode EL2 (Cu)
With respect to the obtained sample, the results of examining the change in resistance when a current was passed in the direction perpendicular to the bonding surface of each layer and the current value was changed are shown in FIGS.

  (1) When the current was swept from +10 mA to -10 mA, a discontinuous change of 3 degrees was observed in the negative current range. (FIG. 37) The threshold values are Ic (σ1; −), Ic (σ2; −), Ic (σ3; −) in order from the largest absolute value.

(2) When the current was swept from -10 mA to +10 mA, a discontinuous change of 3 degrees was observed in the positive current range. (FIG. 38) The threshold values are assumed to be Ic (σ1; +), Ic (σ2; +), Ic (σ3; +) in descending order of absolute value.

(3) Select a current value I1 that satisfies Ic (σ1;-) <I1 <IC (Σ2 ;-). When the current is swept from + 10MA to I1, and then the current is increased in the positive direction, a constant value is obtained from I = I1 to I = IC (Σ3; +), and I = IC (Σ3; +) A discontinuous change was seen. At this time, the resistance value at I> Ic (σ3; +) was different from the values in (1) and (2) (resistance values after (3) in FIG. 37).

(4) A current value I2 that satisfies Ic (σ1; +) <I1 <Ic (σ2; +) is selected. When the current is swept from -10mA to I2, and then the current is decreased (increased in the negative direction), a constant value is obtained from I = I2 to I = Ic (σ3;-), and I = Ic (σ3;- ) Showed a discontinuous change. At this time, the resistance value at I <Ic (σ3 ;−) was a different value from those in (1) and (2) (resistance values after (4) in FIG. 38).

  Even if it is unknown whether σ1; σ2; σ3 is 1, 2 or 3, there is no problem in recording and reproduction. However, it can be seen from the following that σ2 = 3 in this sample. A total of 8 different resistance values were obtained in FIGS. 37 and 38, but the maximum value was shown when I> Ic (σ3; +) in the sweep of (3). At this time, the stored data b should be b [σ1] = 1, b [σ2] = 0, b [σ3] = 1. FIG. 36 shows that σ2 = 3 because the state with the highest resistance is “110”.

  In addition, since the pinned layer FP2 uses a material having a higher spin polarizability than the pinned layer FP1, the free layer FF2 is considered to have a lower inversion current than the free layer FF1. That is, in this embodiment, it is considered that σ1 = 1 and σ3 = 2.

(Third embodiment)
Since the magnetic recording elements according to the first and second embodiments are minute and have a magnetization reversal mechanism, they can be applied to various applications. More specifically, by arranging a large number of these magnetic recording elements, it can be applied to a recording / reproducing apparatus such as an MRAM. Hereinafter, an embodiment related to this will be described.

  FIG. 39 is a diagram schematically showing a cross-sectional structure (part) of the magnetic recording apparatus according to the present embodiment. That is, the magnetic recording apparatus of this embodiment has a structure in which a plurality of magnetic recording elements R are arranged in parallel on an electrode layer (lower layer wiring) WL generally called a word line. The magnetic recording element R is realized by any one of the magnetic recording elements having any configuration of the first and second embodiments. The magnetic recording elements R are electrically insulated from each other by an insulating film I. Each magnetic recording element R is connected to an electrode layer (upper layer wiring) BL generally called a bit line at the top.

  A specific magnetic recording element R can be selected by designating a bit line and a word line.

  Recording on the magnetic recording element R is performed by current flowing from the electrode layer WL through the magnetic recording element R to the electrode layer BL, or current flowing from the electrode layer BL through the magnetic recording element R to the electrode layer WL. Made. Depending on the size, structure, composition, etc. of the magnetic recording element, positive and negative magnetization reversal current values I (i; +) and I (i ;−) are determined for each free layer. As described in the writing section of the first and second embodiments, recording can be performed by applying a write current to the memory cell from 1 to n times.

  The reproduction is performed by passing a current between the electrode layers WL and BL connected to the recording element to be reproduced as in the recording. Details are as described in the section of reading in the first and second embodiments.

The direction of the current at that time may be either direction. During reproduction, the lower limit of the magnetization reversal current Imin = minIc (1; +), ..., Ic (n; +), | Ic (1,-) |, ... , | Ic (n,-) | The recorded information is determined by detecting the voltage or resistance value. Alternatively, a recording state can be determined from a change in current flowing through the recording element by applying a voltage across the recording element to be reproduced.

  As one example (Example 4) of the present embodiment, a magnetic recording apparatus using a magnetic recording element having the same structure as Example 2-1 will be described.

  FIG. 40 shows an example in which one memory cell includes a magnetic recording element R and a selection transistor T. The magnetic recording element R is connected between the bit line BL and one end of the selection transistor T. The other end of the selection transistor T is typically set to the ground potential, and the gate is connected to the word line. For example, the memory cell is manufactured by the following steps. That is, first, the selection transistor T and the lower layer wiring 1 electrically connected to the selection transistor T are formed on the semiconductor substrate by a lithography process, anisotropic etching such as RIE (Reactive Ion Etching), ion implantation, or the like. Is provided. Next, the magnetic recording element R is formed on the lower layer wiring by the same method as described in the first embodiment, and the upper layer wiring BL is further formed on the magnetic recording element R.

  Such memory cells are arranged in a matrix in the memory cell array MCA, and the gates of the select transistors of the memory cells belonging to the same row are connected to the same word line WL. Similarly, the recording elements of the memory cells belonging to the same column are connected to the same bit line BL. A decoder, a readout circuit, and the like are provided around the memory cell array MCA. The bit line BL and the word line WL are connected to a peripheral circuit S such as a decoder and a read circuit.

  The decoder supplies a write current, a reproduction current, and the like to the bit line BL and the word line WL passing through the magnetic recording element R having an address corresponding to an address signal from the outside. That is, at the time of reproduction or recording, the selection transistor T is turned on by selecting the word line of the transistor T connected to the target magnetic recording element R. Next, recording and reproduction are performed by passing a current through the bit line connected to the magnetic recording element R.

  In this embodiment, the selection transistor T is used to select the magnetic recording element R, but other switching elements may be used. If possible, it is preferable that the on-resistance is low. For example, a diode D may be used as shown in FIG. In this case, in each memory cell, the magnetic recording element R and the diode D connected in series are connected between the word line WL and the bit line BL.

  The embodiments of the present invention have been described above with reference to specific examples. However, the present invention is not limited to these specific examples. For example, specific dimensional relations and materials of each element constituting the magnetic recording element, and other shapes and materials such as electrodes, passivation, and insulation structure are appropriately selected from a known range by those skilled in the art. It is included in the scope of the present invention as long as it can be carried out in the same manner and the same effect can be obtained.

  In addition, each component such as an antiferromagnetic layer, an intermediate layer, and an insulating layer in the magnetic recording element may be formed as a single layer, or may have a structure in which two or more layers are stacked.

  In addition, all magnetic recording elements and magnetic recording devices that can be implemented by those skilled in the art based on the magnetic recording elements and magnetic recording devices described above as the embodiments of the present invention are also included in the gist of the present invention. As long as it is included, it belongs to the scope of the present invention.

  In addition, in the category of the idea of the present invention, those skilled in the art can conceive various changes and modifications, and it is understood that these changes and modifications also belong to the scope of the present invention. .

1 is a schematic cross-sectional view of a magnetic recording element according to a first embodiment of the present invention. FIG. 3 is a schematic cross-sectional view for explaining a method of writing 2-bit information in the magnetic recording element of the first embodiment. FIG. 4 is a diagram for explaining a current writing process, in which the left column shows the code of the magnetic recording element before current writing, and the right column shows the code of the magnetic recording element 10 after current writing. FIG. 4 is a diagram for explaining a current writing process, in which the left column shows the code of the magnetic recording element before current writing, and the right column shows the code of the magnetic recording element 10 after current writing. FIG. 4 is a diagram for explaining a current writing process, in which the left column shows the code of the magnetic recording element before current writing, and the right column shows the code of the magnetic recording element 10 after current writing. FIG. 4 is a diagram for explaining a current writing process, in which the left column shows the code of the magnetic recording element before current writing, and the right column shows the code of the magnetic recording element 10 after current writing. FIG. 4 is a diagram for explaining a current writing process, in which the left column shows the code of the magnetic recording element before current writing, and the right column shows the code of the magnetic recording element 10 after current writing. It is a figure for demonstrating an electric current writing process, the left column shows the code | symbol which the magnetic recording element before electric current writing has, and the code | symbol which the right column shows the code | symbol which the magnetic recording element after electric current writing has. A current supply timing chart for current writing. 10A and 10B illustrate a method for selecting a write current value. Sectional schematic diagram for demonstrating each recording state and the electrical resistance of an element. The cross-sectional schematic diagram for demonstrating the modification of fixed layer FP1 or free layer FF1, FF2. Sectional schematic diagram for demonstrating another modification of fixed layer FP1 or free layer FF1, FF2. Sectional schematic diagram for demonstrating another modification of fixed layer FP1 or free layer FF1, FF2. Sectional schematic diagram for demonstrating another modification of fixed layer FP1 or free layer FF1, FF2. Sectional schematic diagram for demonstrating another modification of fixed layer FP1 or free layer FF1, FF2. Sectional schematic diagram for demonstrating another modification of fixed layer FP1 or free layer FF1, FF2. Sectional schematic diagram for demonstrating another modification of fixed layer FP1 or free layer FF1, FF2. Sectional schematic diagram for demonstrating another modification of fixed layer FP1 or free layer FF1, FF2. Sectional schematic diagram for demonstrating another modification of fixed layer FP1 or free layer FF1, FF2. Sectional schematic diagram for demonstrating another modification of fixed layer FP1 or free layer FF1, FF2. Sectional schematic diagram for demonstrating another modification of fixed layer FP1 or free layer FF1, FF2. Sectional schematic diagram for demonstrating another modification of fixed layer FP1 or free layer FF1, FF2. Sectional schematic diagram for demonstrating another modification of fixed layer FP1 or free layer FF1, FF2. Sectional schematic diagram for demonstrating another modification of fixed layer FP1 or free layer FF1, FF2. Sectional schematic diagram for demonstrating another modification of fixed layer FP1 or free layer FF1, FF2. The figure which shows the relationship between the thickness of a nonmagnetic layer, and the exchange coupling strength between the two ferromagnetic layers laminated | stacked through the nonmagnetic layer. FIG. 6 is a schematic cross-sectional view showing a modification of the magnetic recording element of the first embodiment. FIG. 6 is a schematic cross-sectional view showing another modification of the magnetic recording element of the first embodiment. FIG. 6 is a schematic cross-sectional view showing another modification of the magnetic recording element of the first embodiment. FIG. 6 is a schematic cross-sectional view showing another modification of the magnetic recording element of the first embodiment. FIG. 6 is a schematic cross-sectional view showing another modification of the magnetic recording element of the first embodiment. The figure which shows the resistance value in each electric current value of a magnetic-recording element at the time of sweeping an electric current from Imax> 0 to Imin <0 about a 1st Example. The figure which shows the resistance value in each electric current value of a magnetic-recording element at the time of sweeping an electric current from Imin <0 to IMAX> 0 about a 1st Example. Sectional schematic diagram for demonstrating the magnetic-recording element based on the 2nd Embodiment of this invention. FIG. 6 is a schematic cross-sectional view showing the relationship between recording magnetization, resistance value, and recorded information sign in a magnetic recording element according to a second embodiment. The figure which shows the change of resistance when a current is swept from positive to negative in the direction perpendicular to the bonding surface and the current value is changed in the magnetic recording element according to Example 3 of the present invention. The figure which shows the change of resistance when current is swept from negative to positive in the direction perpendicular to the bonding surface and the current value is changed in the magnetic recording element according to Example 3 of the present invention. FIG. 9 is a schematic cross-sectional view showing the periphery of a magnetic recording element of a magnetic recording apparatus according to Example 4 of the invention. FIG. 9 is a schematic diagram showing a circuit configuration of a magnetic recording apparatus according to Embodiment 4 of the present invention. FIG. 9 is a schematic diagram showing a circuit configuration of a magnetic recording apparatus according to Embodiment 4 of the present invention.

Explanation of symbols

FF1, FF2 ... Free layer
FP1 ・ ・ ・ Fixed layer
SL1, SU2 ・ ・ ・ Nonmagnetic layer

Claims (4)

It has a magnetic layer (recording layer) whose magnetization direction is variable,
Spin-polarized electrons are injected, and the magnetization direction changes according to the direction of spin-polarized current flow,
A magnetic recording element capable of recording information according to the magnetization direction,
A first magnetic layer (recording layer) having a variable magnetization direction;
A first nonmagnetic layer formed on the first recording layer;
A pinned layer formed on the first nonmagnetic layer, including a magnetic material, and having a magnetization direction fixed;
A second nonmagnetic layer formed on the pinned layer;
A second magnetic layer (recording layer) formed on the second nonmagnetic layer and having a variable magnetization direction;
With
The positive and negative reversal current critical values of the first magnetic layer are Ic (1; +), Ic (1 ;-),
When the positive and negative reversal current critical values of the second magnetic layer are Ic (2; +) and Ic (2 ;−),
A magnetic recording element characterized by Ic (1; +)> Ic (2; +) and | Ic (1 ;-) |> | Ic (2 ;-) | . 2. The magnetic recording element according to claim 1, wherein two recording layers have different thicknesses.   A magnetic recording device comprising the magnetic recording element according to claim 1. It has a magnetic layer (recording layer) whose magnetization direction is variable,
Spin-polarized electrons are injected, and the magnetization direction changes according to the direction of spin-polarized current flow,
A magnetic recording element capable of recording information according to the magnetization direction,
A first magnetic layer (recording layer) having a variable magnetization direction;
A first nonmagnetic layer formed on the first recording layer;
A pinned layer formed on the first nonmagnetic layer, including a magnetic material, and having a magnetization direction fixed;
A second nonmagnetic layer formed on the pinned layer;
A second magnetic layer (recording layer) formed on the second nonmagnetic layer and having a variable magnetization direction;
With
The positive and negative reversal current critical values of the first magnetic layer are Ic (1; +), Ic (1 ;-),
When the positive and negative reversal current critical values of the second magnetic layer are Ic (2; +) and Ic (2 ;−),
Magnetic recording element satisfying Ic (1; +)> Ic (2; +) and | Ic (1 ;−) |> | Ic (2 ;−) |
The positive write currents Iw (1; +) and Iw (2; +) are set to values satisfying Iw (1; +)> Ic (1; +)> Iw (2; +)> Ic (2; +)
Negative write currents Iw (1 ;−), Iw (2 ;−) are set to values satisfying Iw (1; −) <Ic (1; −) <Iw (2; −) <Ic (2 ;−)
When writing the data strings b [1] (= 0 or 1) and b [2] (= 0 or 1) in order from the first magnetic layer and the second magnetic layer having a large reversal current,
when writing b [1] = 0, b [2] = 0, a step of passing a write current Iw (1 ;−);
when writing b [1] = 1, b [2] = 1, a step of passing a write current Iw (1; +);
When writing b [1] = 0 and b [2] = 1, first, a write current Iw (1; +) is passed, and then a write current Iw (2 ;−) is passed;
When writing b [1] = 1, b [2] = 0, first, a write current Iw (1 ;−) is passed, and then a write current Iw (2; +) is passed;
A magnetic recording method comprising:

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